I have a 2000 Dodge Pick-up with a 5.2, my problem is it keeps throwing the #8 cylinder misfire code, as I drive it, it will start to spit and sputter and fall flat on its face, so times it will do it when its hot or when its cold (engine temp ) but it will always do it within 10 -15 miles of start-up. So far I have replaced Cap Rotor, fuel injector, swapped plugs and wires, new IAC, new TPS, and it keeps throwing the code. I have read and fully understood the TSB for the spark plug wire routing. I have done a compression test on the motor with all plugs removed and have an acceptable readings on all ciylinders and # 8 is 155. I will state and that the # 8 spark plug always shows oil on it when I remove it from the head even if it only has run for 2-3 minutes ( not oil fouled but oily ).

 

2 thoughts:

Clogged Catalytic converter. As the Cat heats up the exhaust backs up into the first cylinder it reaches #8. try running with the forward O2 sensor out of its bung, this will allow the excess pressure out, but it will obviously throw an o2 sensor code. If the misfire goes away, that could be your problem.

A bad Precat O2 sensor may also be the problem. The O2 sensor isn't used to control fuel until after is heats up to operating temperature. Replace it and see if the problem goes away.

 

Also, have you checked the plenum gasket?

Million threads on that problem in the forum.

 

yup, i second the plenum gasket, ive seen this problem come up a few times, and it was the plenum fouling the #8 cylinder with oil.


or the dreaded cracked head....get a compression test done.